Video motion detection systems are known in which a comparison is made between a live video image and a stored representation of an earlier video image in order to detect relative motion between the two signals on the basis of a difference between the live and stored images. In order to reduce the information storage and processing overhead needed to compare video images, and to reduce sensitivity to relatively minor fluctuations between images, a live video signal can be analyzed to produce a first statistical quantity that is then compared to a second statistical quantity that is representative of a previous video signal.
U.S. Pat. No. 4,894,716, assigned to Burle Technologies, Inc., the assignee of the present application, describes a motion detection system wherein the positions of edges of objects within a live video image are compared with stored data relative to edge positions within the image at an earlier time. In that motion detection system, sensitivity to minor changes is reduced by detecting changes over several adjacent horizontal portions of an image before an alarm is activated. In general, increasing the size of portions of the image from which image statistics are extracted and compared reduces sensitivity to minor or spurious image changes.
In addition to detecting whether motion has occurred, it would be desirable for a video motion detection system to determine the location or locations within the video image where motion is detected. Such capability could be used, for example, to produce an alarm in response to detecting motion within a selected portion or portions of the image while ignoring motion within other non-selected portions of the image. It would further be desirable to provide such a motion detection system in which the spatial resolution is high enough to allow precise definition of the selected area or areas that are analyzed for motion and the selected area or areas that are to be ignored. However, improvement of the spatial resolution of motion detection has heretofore been in conflict with the extraction of sufficient relevant statistical quantities from a relatively large portion of the image in order to reduce sensitivity to minor or insignificant changes.